The present invention relates to a printed circuit board connection structure, and, more particularly, to a backplane connection configuration for the connection of a plurality of voltage levels to each of a plurality of printed circuit boards, and to a mechanism for the extraction and insertion of individual printed circuit boards into a backplane.
Previous designs for logic system backplanes, in which signals at more than one voltage level had to be processed, have employed a connector on the front card edge for high voltage levels or middle voltage levels and a separate connector attached to the backplane for low voltage, usually logic, signals. For example, the controller disclosed in U.S. Pat. No. 4,250,563, issued Feb. 10, 1981 to Struger, has input/output terminals wired to swing arm connectors on the front of the controller. This front card edge wiring must be installed manually, point-to-point, upon each board. This manual wiring step requires considerable time and a skilled operator to perform the necessary connections.
The power-on removal of printed circuit boards from conventional backplane connectors has involved the operation by maintenance personnel of disabling switches or similar equipment to ensure that the backplane contacts will not arc upon removal of the printed circuit board. For example, some prior art systems include toggle switches mounted upon each printed circuit board, which require that the maintenance personnel operate the switch prior to removal or insertion of the printed circuit board into the backplane. Failure to ensure that the switch is properly positioned prior to insertion or removal of the board results in the board being inserted or removed with some circuits in a current carrying condition. This can result in arcing and, in extreme cases, destruction of the printed circuit board contacts and the backplane connector contacts, especially for the high voltage contacts. With a large number of boards to be removed and/or inserted, there is an increase in the possibility that one or more of the switches would not be operated due to operator inattention or oversight. In U.S. Pat. No. 4,245,270 issued Jan. 13, 1981 to Busby, a phased power-down for circuit board removal is disclosed. However, the system disclosed by Busby allows removal of circuit boards without first shutting down each circuit, and each circuit may be decoupled while in a current carrying condition. Further the logic circuits may experience rapid output level changes resulting in sequencing of memory elements. Damage or destruction of the contacts on the printed circuit board or the backplane connector can require that the entire system be shut down while repairs are made. In a control system in which printed circuit boards are used to control many system operations, it is desirable, and essential in systems including critical control functions, to be able to replace a single circuit board or several circuit boards in a system without shutdown of the entire system and without requiring the maintenance person to manually operate a disabling circuit.